At the present time basically three different methods are used for the detection of storms:
a) Detection by ionisation of the air or corona effect.
b) Detection by radiofrequency.
c) Detection by measurement of the electrostatic field.
The basic operating principle of each of these detection methods is described hereunder.
a) Storm detector by ionisation of the air or corona effect.
A detector of this type is described in the Spanish patent application published under the number ES-A-2038551.
This type of detectors act by measuring the current produced by the variations of electric field caused by the storms and, more specifically, the abrupt variations which take place moments before lightning strikes. The main drawback with this type of detector is that they only detect abrupt variations of the field, for which reason its forewarning time of the storm is almost nil, since they only detect the activity of the storm when the latter is over the actual detector.
b) Storm detector by radiofrequency.
An example of a detector of this type is described in the European patent EP-B-0252807 (the translation of which into Spanish has been published under the number ES-T-2030747).
The radiofrequency detectors detect the radiofrequency emissions which the lightning emits when passing through the atmosphere from the cloud to the ground. The detectors of this type, although they are very effective for detecting storms at long distance, have one drawback: they are unable to detect storms that are in formation just above the detector itself since they only detect the storm when this has a considerable electric activity.
c) Storm detector by measurement of the electrostatic field.
It is the only detector capable of continuously measuring the electrostatic field, for which reason it can measure the small variations or increments in the electrostatic field produced both by the approach of a storm and by the creation of the latter over the detector itself. The main drawback of this type of detector is not in the method of detection but in the detection instruments that are used at the present time. These instruments, for example that described in the French patent application published under the number FR-A-2432719, are based on the principle of the field mill. The instrument described in FR-A-2432719 uses a mechanical motor to transform the electrostatic field into an alternating signal, which is much easier to measure. The use of a motor implies a drawback, since when using moving parts, there is the risk of breakdown and wear (especially if it is kept in mind that this type of instrument often has to be working 24 hours a day, 365 days a year).
For this reason, it has been considered that it would be desirable to provide a device or system useful for measuring the electrostatic field and which does not have this type of moving elements.